The present invention is related to hydrogen sensors, and more particularly, to a robust single-chip hydrogen sensor and method for manufacturing the same.
During the early 1990s, Sandia National Laboratory developed a single-chip hydrogen sensor that utilized Palladium-Nickel (PdNi) metal films as hydrogen gas sensors. U.S. Pat. No. 5,279,795, naming Robert C. Hughes and W. Kent Schubert as inventors, assigned to the United States as represented by the U.S. Department of Energy, describes such a sensor and is incorporated by reference herein.
One of the key benefits of the sensor described in the ""795 patent is its ability to detect a dynamic range of hydrogen concentrations over at least six orders of magnitude. Prior solutions to the problem of detecting hydrogen concentrations had been generally limited to detecting low concentrations of hydrogen. These solutions include such technologies as metal-insulator-semiconductor (MIS) or metal-oxide-semiconductor (MOS) capacitors and field-effect-transistors (FET), as well as palladium-gated diodes.
The hydrogen sensor described in the ""795 patent was a notable advance in hydrogen-sensing technology. It was, however, primarily limited to an experimental laboratory environment due to the difficulties encountered in manufacturing such a sensor.
In typical silicon fabrication facilities, metal films are first blanket-deposited across the entire wafer, and are subsequently patterned by an etch process. However, conventional etchants for PdNi also attack aluminum, which is present on the wafer surface as an interconnect metal before the PdNi film is deposited. Patterning the PDNI by etching would also attack the unprotected aluminum, destroying the sensor. Even some non-conventional semiconductor fabrication techniques involving the use of a photoresistive material applied before the PdNi in a xe2x80x9clift-offxe2x80x9d process have produced very low yields in tests performed by the assignee of the present invention. Low yields in the production of semiconductor devices typically translates to difficulties in producing a commercializable product.
It would be desirable to provide a robust single-chip hydrogen sensor that is capable of sensing hydrogen concentrations over a broad range, such as from less than 1% to approximately 100% concentrations.
It would also be desirable for such a sensor to be efficiently manufacturable, so that costs are reduced and the sensor is producible in high enough yields to enable commercialization.
It would be desirable for such a sensor to provide measurement results that approximate or improve on the results from previous hydrogen sensors.
It would additionally be desirable to minimize sensor drift and to improve device-to-device and wafer-to-wafer repeatability.
In accordance with an illustrative embodiment of the present invention, some of the problems associated with manufacturing a robust hydrogen sensor are addressed.
Various embodiments of the invention provide a robust single-chip hydrogen sensor and a method for fabricating such a sensor. By adding an adhesion-promoting layer between the body of a sensor and an on-chip resistive hydrogen-sensing element, device yields are improved when compared to directly applying the resistive hydrogen-sensing elements to the sensor body.
According to a preferred embodiment of the present invention, the adhesion-promoting layer is a chromium (Cr) adhesion layer, and the resistive hydrogen-sensing element is a PdNi alloy.